It is becoming more and more desired and customary, particularly, for example in the case of television broadcasting and videograms, that the finally edited picture material, as ready for transmission or viewing, shall be in the form of colour video tape. In some cases the picture material can be shot originally on colour film, and in other cases on colour video tape. In the latter case it may seem a natural course to do the editing using video tape techniques, since both the original material and the desired end-product are both video tapes. Also in the former case it may appear that the simplest procedure is to copy the original film material onto a video tape and then to edit the tape using video tape techniques. Such video tape editing, generally called video transfer editing, is performed by copying desired sections of the original video tape onto a new recording tape in given positions thereon, so that the specific desired sections, or scenes, are obtained in the order desired. Although this editing technique may appear to be relatively simple, it is often desirable to be able to carry out the editing work on film material. One reason for this is the possibility then afforded of employing the accurate and simple sound processing techniques well tried in film editing. There is also to be found with producers and in film laboratories and like establishments vast quantities of film-recording and film-editing equipment whose continued use is highly desirable for economic reasons. Another reason is that many editors consider themselves capable of producing a much better result, both qualitatively and artistically, when editing film material than when editing video tape. In this case, however, the necessary preparation of a colour video tape, which is the desired end product, in exact conformity with the finally edited film work print, the so-called video tape conforming, creates certain problems, deriving from the construction of the colour video signal.
Quite apart from its content of visual information, which has the nature of a succession of images corresponding to the picture frames of a motion picture film, the video signal is constructed to include also periodic signal components which extend over a plurality of successive images. When considering, for example, the PAL-system generally used for colour video in Europe and in a host of other countries, it is found that the video signal is so constructed as to comprise for each complete image, corresponding to a picture frame in a motion picture film, two immediately sequential half-images, so-called video fields. In addition, the video signal also includes a periodically repeated signal component with a period extending over four such video fields, i.e. over two complete images corresponding to two film frames, and a further, periodically repeated signal component with a period extending over eight video fields, i.e. over four complete images corresponding to four film frames, and which is synchronized with the first mentioned signal component extending over four video fields, i.e. has a fixed phase position relative said first mentioned signal component. The video technique has as an absolute condition that no interruptions or discontinuities appear in the first signal component with a period of four video fields, and that in order to obtain a perfect result when showing the video tape, neither should any discontinuities occur in the second signal component with a period of eight video fields. Neither should there be any deviations in the predetermined, mutual phase position between the 4-field sequence signal and the 8-field sequence signal. This presents normally no serious problem when editing from video tape using the aforementioned video transfer editing technique, since the professional video recording equipment used will automatically ensure that the aforementioned conditions are fulfilled by the recorded video signal. If the editor orders a scene transition "cut" between two sequential scenes at a location such that the aforementioned conditions concerning the 4-field sequences and 8-field sequences would not be satisfied by the recorded video signal, the recording equipment will automatically displace the scene transition or "cut" to a location where said conditions will be fulfilled, i.e. so that the last video field of a preceding scene and the first video field of the immediately following scene are those which follow each other immediately in the predetermined periodic field sequence of the video signal. Normally, such a displacement of the "cut" is not detrimental to the editing work, since the result can be seen and assessed directly; moreover any sound recording present will be displaced to exactly the same extent, thereby to maintain the synchronization between sound and picture.
This problem, however, is extremely troublesome when conforming a colour video tape with an edited film work print and associated sound track. Admittedly, the video recording equipment used will ensure, in the aforesaid manner, that the scene transitions or "cuts" between the various scenes on the conformed video tape are so located as to satisfy the said conditions concerning the periodic video field sequences, but the displacement of the "cuts" necessary herefor during the video tape conforming process has as result that said "cuts" will no longer have exactly the same positions as the scene transitions or cuts in the edited film work print. Consequently, the locations of the scene transitions, often chosen with great care by the editor, will be displaced, which can naturally be regarded as a serious error. A more serious disadvantage is that the automatic displacement of the scene transitions carried out by the video recording equipment in order to fulfill the aforesaid conditions concerning the video signal, results in a lack of synchronism between picture and sound, the sound in this case not being displaced to the same extent as the picture images. Such asynchronism cannot be accepted.
As will readily be understood, the above problem cannot be solved by transferring the edited film, the so-called work print, directly onto a video tape by means of a so-called telecine equipment, since the damage caused to the film during the editing process prevents a video tape of acceptable quality being obtained. One possible method would be to conform a faultless film material in a conventional manner, into exact agreement with the edited film work print, and to transfer said conformed film onto a video tape by means of a telecine. The production work involved in such a method, however, is extremely time consuming, requiring two similar film copies to be made from the originally taken picture material, of which copies one is used as the work print and the other for the subsequent film conforming. When the original picture material is on film, it is thus necessary to produce an additional work print on film, while when the original picture material is on video tape, it is necessary to produce from said tape two film copies. Much time and expense is incurred in both instances.